1. Field of the Invention
The present invention relates to a cooling fan structure for rotary electric machines. More particularly, the present invention relates to a cooling fan structure suitable for use with devices such as alternators.
2. Related Art
Japanese Patent Application Laid-open publication No. 63-265545 discloses alternators having installed therein axial fans with a shroud at each edge. The shrouds are fastened at each end of the peripheral axial flow wings so as to favorably cool a rotor without directing cooling air in a centrifugal direction.
Today's alternators have centrifugal fans at the ends of the rotor core. The centrifugal fans consist of a plurality of centrifugal blades arranged in a radial configuration for cooling a coil-end of stator coils. Centrifugal cooling air that had begun to flow in centrifugal direction favorably cools the end of the stator coil, which has a poor cooling condition when at rest.
However, the prior art described above and presently known to the inventors of the subject application has the drawback that the stator coil of the alternator is not sufficiently cooled.
Furthermore, some prior art devices have an increased chance of suffering from fluid pressure losses and sharp decreases in cooling air flow rates due to the eddy created by the curvature and swing motion of the cooling air in the vicinity of the inside portions at the end of stator coil. The positional relationship between the centrifugal blades and the end of the stator coil influences the cooling ability of the stator coil and therefore limits the magnetic circuit design. When the stator coil is not cooled properly, the magnetic resistance increases, and to achieve the same output power requires a larger magnetic circuit.